[Monoclonal gammopathy of (un)known significance]

Monoclonal gammopathies are a frequently diagnosed entity. However, the diagnosis is not always clinically relevant. The diagnosis of a monoclonal gammopathy requires serum electrophoresis, immunofixation and free light chain measurement. Sometimes, monoclonal gammopathies occur in the course of transient or autoimmune inflammation. Further diagnostics should only be performed after risk assessment according to Mayo criteria. In non-low risk patients, a symptomatic myeloma has to be ruled out via SLiM-CRAB criteria. The diagnostic work-up should include whole-body MRI and a bone marrow puncture as well as a 24 h urine sample. If it does not imply myeloma, the diagnosis of MGUS is confirmed and a follow-up after 6 months is recommended. After that, low-risk patients only need SLiM-CRAB screening at clinical signs of progression. All other patients should receive serologic follow-ups once a year. Importantly, MGUS patients show higher morbidity. Amongst a higher prevalence of osteoporosis and immunodeficiency, a wide array of MGUS-associated diseases such as AL amyloidosis, deposition diseases and Fc binding-dependent effects can occur. This article gives an overview over the work-up, observation and caveats of monoclonal gammopathy of (un)known significance.